This proposal describes experiments designed to develop the murine plasmacytoma MOPC 315 as a model for the study of the mechanism whereby hormones regulate the rate of synthesis of rRNA. I propose to determine if hormones increase the amount of RNA polymerase I within the cell. In addition, transcription experiments will be carried out in vitro to determine if hormones alter the affinity with which the pol I binds ribosomal DNA promoters.